Question

I am declaring a String array as:

String[] items1 = new String[5];
String[] items2 = new String[20];

How much effect both of these arrays will produce on memory and performance if both contain only 2 elements.

Answer 1

You can test this yourself.

public static void main(String... args) {
    long free1 = free();
    String[] two = new String[2];
    long free2 = free();
    String[] twenty = new String[20];
    long free3 = free();
    if (free3 == free1) System.err.println("You need to use -XX:-UseTLAB");
    System.out.println("String[2] took " + (free1 - free2) + " bytes and String[20] took " + (free2 - free3) + " bytes.");
}

private static long free() {
    return Runtime.getRuntime().freeMemory();
}

prints

String[2] took 24 bytes and String[20] took 96 bytes.

So you could be wasting 72 bytes of memory. If your memory cost $10 per GB, you could be wasting 0.000072 cents of memory. However, a second of your time could be worth 2 cents. In this case it is literally not worth spending a milli-second worrying about it in this case. i.e. The time it takes to write 20 instead of 2 is worth far, far more.